Improved lamp color temperature stability in an automated luminaire

ABSTRACT

Described is dynamic control of the temperature of the envelope of an HID lamp in order to stabilize the output color temperature of the lamp. As the lamp power is changed, or environmental factors alter the lamp envelope temperature, the system senses these changes and adjusts the lamp cooling systems so as to move the lamp envelope temperature back to the desired point.

RELATED APPLICATION

The present application claims priority to provisional application62/058,551 filed 1 Oct. 2014.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to the control of the colortemperature of a lamp, and more specifically to the color temperature ofa high intensity discharge lamp as utilized in an automated luminaire.

BACKGROUND

Luminaires with automated and remotely controllable functionality arewell known in the entertainment and architectural lighting markets. Suchproducts are commonly used in theatres, television studios, concerts,theme parks, night clubs and other venues. A typical product willcommonly provide control over the pan and tilt functions of theluminaire allowing the operator to control the direction the luminaireis pointing and thus the position of the light beam on the stage or inthe studio. Typically this position control is done via control of theluminaire's position in two orthogonal rotational axes usually referredto as pan and tilt. Many products provide control over other parameterssuch as the intensity, color, focus, beam size, beam shape and beampattern. FIG. 1 illustrates a typical multiparameter automated luminairesystem 10. These systems typically include a plurality of multiparameterautomated luminaires 12 which typically each contain on-board a lightsource (not shown), light modulation devices, electric motors coupled tomechanical drives systems and control electronics (not shown). Inaddition to being connected to mains power either directly or through apower distribution system (not shown), each luminaire is connected inseries or in parallel to data link 14 to one or more control desks 15.An operator typically controls the luminaire system 10 through thecontrol desk 15.

To achieve the high brightness needed for such systems it is common toutilize High Intensity Discharge lamps (HID). Short and medium arc HIDlamps produce light from a plasma cloud produced by an electrical arcthat is maintained between two adjacent electrodes within a sealedquartz envelope. FIG. 2 shows an example 30 of an HID lamp that may beused. Electrodes 32 and 33 are enclosed within sealed quartz envelope 38and connected by lead wires 35 to a base 36 and electrical connections37. The HID lamps used in entertainment lighting luminaires often usevery small arc gaps 34 between the two electrodes, of the order of 1 to5 mm, to provide a low etendue light source that facilitates the designof a high quality optical system for projecting images and colors. Thespectrum of light emitted by the lamp is produced by the ionization andemission of a mix of rare earths and gases that are contained within theenvelope 38. The emission spectra of each of these components, whenheated to the plasma temperatures of the arc, combine to produce anoverall emission spectrum for the lamp. The lamp manufacturer carefullyselects the mix of constituents for the lamp fill in order to produce awhite light output with a spectrum that approximates to that of a blackbody emitter at the desired color temperature. For example, it is commonto manufacture HID lamps with a target color temperature of 5600 K, ordaylight. It is also common to produce lamps with target colortemperatures of 3200 K, 7000 K, 10000 K and other white points ascommonly used in the entertainment lighting business for televisioncameras, film cameras or a live audience.

A significant problem with such lamps is maintaining the stability ofthe desired target color temperature. Small changes in the arc gap, asthe electrodes burn away, and fluctuations in the temperature of thelamp envelope can make significant changes to the precise mix ofconstituents that are emitting spectra to the combined spectrum. Forexample, as the temperature drops within the envelope then someconstituents that emit specific wavelengths of light may drop out of theionization cloud, or alter their output, thus affecting the resultantoutput spectrum and thus the output color temperature. Lampmanufacturers may attempt to mitigate this variability by enclosing theinner quartz envelope 38 within a second outer envelope (not shown) toprovide rudimentary temperature control. However, such designs are stillnot stable and the color temperature may vary significantly.

It is also common to desire to change the power consumed by the lamp, inorder to control its brightness. Unfortunately any change in lamp poweralso affects the operating temperature of the lamp that, in turn, willaffect the output color temperature. Prior art systems have utilized fancooling systems to attempt to stabilize the lamp temperature, but thesehave been ineffective and slow to operate, allowing large changes in thelamp output color temperature that were visible to the audience.

It would be advantageous to provide a system that was capable ofproviding continuous and dynamic control of the temperature of theenvelope of an HID lamp in order to stabilize the output colortemperature of the lamp.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings in which likereference numerals indicate like features and wherein:

FIG. 1 illustrates a typical prior art automated lighting system;

FIG. 2 illustrates a typical HID lamp; and;

FIG. 3 illustrates an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are illustrated in theFIGUREs, like numerals being used to refer to like and correspondingparts of the various drawings.

The present invention generally relates to the control of the colortemperature of a lamp, and more specifically to the color temperature ofa high intensity discharge lamp as utilized in an automated luminaire.

In one embodiment the present invention utilizes a tightly temperaturecontrolled enclosure 40 for the HID lamp in order to maintain the lampenvelope temperature within close tolerances and thus maintain the colortemperature of the light output from the lamp within close tolerances.

FIG. 3 illustrates one embodiment of the invention. High IntensityDischarge (HID) lamp 30 comprising electrodes 32 and 33 that areenclosed within sealed quartz envelope 38 and connected by lead wires 35to a base 36. Base 36 may connect to lamp connector 44 from whichelectrical connections may be made to the control gear (not shown). Inoperation an electrical arc is formed across arc gap 34 creating alocalized region containing high temperature plasma. This plasma excitesthe mix of rare earths and gases that are contained within envelope 38such that a distinctive light spectrum is emitted. The constituentspectra forming the light output spectrum are sensitive to thetemperature of the envelope 38. Lamp 30 is contained within enclosure 40providing a controlled environment. Air may enter enclosure 40 throughcontrollable fan or blower 42 b and may exit the enclosure throughcontrollable fan or blower 42 a. Light from lamp 30 may be directed andcontrolled by reflector 41. One face of the enclosure 46 may be a windowmanufactured of a transparent material for the light from lamp 30 andreflector 41 to exit. Transparent window 46 may be planar, curved,faceted or any shape as known in the art. Transparent window 46 may beglass, quartz or other transparent material. Transparent window 46 mayhave coatings including but not limited to, dichroic hot mirror, coloreddichroic, heat resistant coatings.

Enclosure 40 may further comprise a plurality of temperature sensors; 48a, 48 b, 48 c, 48 d, and 48 e. These temperature sensors are configuredto read the temperature of critical points of the lamp, its enclosure,and the exiting and entering air. For example, temperature sensor 48 aand 48 c may measure the temperature at different points in enclosure40. Temperature sensor 48 e may measure the temperature of lamp base 36or the lamp pinches. Temperature sensor 48 b may measure the temperatureof incoming air through controllable fan 42 b, and temperature sensor 42a may measure the temperature of exiting air through controllable fan 42a. Additionally remote temperature sensors, such as 48 f, may beutilized elsewhere in the luminaire as desired.

In operation all temperature sensors 48 a-48 f, controllable fans 42 aand 42 b are connected to and controlled by a central controller 50. Inmanufacturing and testing controller 50 may be configured with knowledgeof the configuration of enclosure 40, lamp 30, and the positions andparameters of temperature sensors 48 a-48 f and fans 42 a and 42 b. Thisknowledge includes the time constants of the various connected items,and the amount of time it takes to heat or cool lamp envelope 38 andlamp pinches as a function of lamp power, temperatures, and fan speeds.Algorithms in controller 50 may be configured so as to operatetemperature control of enclosure 40, and thus lamp envelope 38, as aparameterized closed loop system such that all temperatures aremonitored and fan speeds raised and lowered as needed to keep thetemperature of lamp envelope 38 at a constant point.

The control system has access to a lighting plan that includes theplanned lamp power when the lamp is being dimmed or undergoing otheractivities that may affect envelope temperature as a function of time,such that it can pro-actively adjust fan speeds to allow for a predictedtemperature change that will occur from any particular change in lamppower. For example, a particular lamp may be operated at 1700W, 1500W,1200W, 900W or other wattage while maintaining a constant lamptemperature, and thus a constant light output color temperature. Inother embodiments maintaining color temperature constant may requirevariation in the lamp temperature.

In a further embodiment the lamp may be configures to run at anextremely low power when the unit is shuttered or in blackout with nolight emerging. In prior art products this led to a significantlylowered lamp temperature that, in turn, produced a much higher outputcolor temperature. When the lamp was opened up from blackout and raisedback to full power, this high color temperature was noticeable as wasthe change in color temperature as the lamp warmed up and wasobjectionable to the viewer or television camera. However, with thesystem of the invention, controller 50 may recognize the blackoutcondition and automatically lower fan speeds sop that the lamptemperature remains at the correct level. Then, when the lamp is openedup from blackout the color temperature of the output light will becorrect and stable.

In further embodiments of the invention different numbers and positionsof temperature sensors are used.

A particular style of single ended HID lamp is illustrated in FIG. 3.The invention is not so limited and any style of lamp, single ended,double ended, integral reflector, and other lamp styles as known in theart could be used in an embodiment of the invention.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisinvention, will appreciate that other embodiments may be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

The invention has been described in detail, it should be understood thatvarious changes, substitutions and alterations can be made heretowithout departing from the spirit and scope of the invention asdescribed by the appended claims

We claim:
 1. An automated luminaire comprising: a light source thatgenerates different color temperature light based on variance in itsoperating conditions; an enclosure for the light source with fan(s)which gate the flow of air into and out of the enclosure; temperaturesensor(s) which monitor temperatures that effect the temperature insidethe enclosure; controller that monitors power to the lamp as a functionof time historically and prospectively based on a preprogrammed lightshow and operating temperature and controls airflow to maintainoperating temperature given power applied to the lamp to optimize aconstant lamp output color temperature as a function of time.
 2. Anautomated luminaire comprising: a light source that generates differentcolor temperature light based on variance in its operating conditions;an enclosure for the light source with fan(s) which gate the flow of airinto and out of the enclosure; temperature sensor(s) which monitortemperatures that effect the temperature inside the enclosure;controller that monitors power to the lamp and operating temperature andcontrols airflow to maintain operating temperature given power appliedto the lamp so that the lamp output color temperature is maintained asconstant.
 3. The luminaire of claim 2 where the temperature in theenclosure is maintained as constant independent of power applied.
 4. Theluminaire of claim 2 where the target temperature in the enclosuredepends on the driving power applied to the lamp.
 5. The luminaire ofclaim 2 where the temperatures monitored includes the temperature in theenclosure, and the input air temperature
 6. The luminaire of claim 2where the temperatures monitored includes the temperature in theenclosure, and the input air temperature and the output air temperature.7. The luminaire claim 2 where the temperatures monitored includes thetemperature in the enclosure, and the input air temperature and theoutput air temperature the ambient air temperature.
 8. The luminaireclaim 2 where the temperatures monitored includes the temperature at aplurality of locations in the enclosure.
 9. The luminaire claim 2 wherethe temperatures monitored includes the temperature at the lamp base.